Krejcikova won 7-6 (8-6) 6-3 in a back-and-forth battle lasting one hour and 50 minutes.
Both players were appearing in the last eight of a grand slam for the first time, with 17-year-old Gauff having not dropped a set in reaching this stage.
She had the advantage for much of the first set but fell apart towards the end and then allowed Krejcikova to build a huge second-set lead that was too big to claw back.
— wta (@WTA) June 9, 2021
World number 33 Krejcikova will play either defending champion Iga Swiatek or Maria Sakkari in the last four, as Gauff paid the price for making 41 unforced errors.
Gauff, seeded 24, led 3-0 and 5-3 in the opening set but was pegged back on both occasions.
One set point had already been lost before she failed to convert two more in a pivotal game lasting over seven minutes at 6-5 as her Czech opponent somehow held on to force a tie-break.
There were nerves on both sides of the court in the breaker until Gauff forged ahead at 6-4, but her fourth and fifth set points were both scuppered by fine forehand winners from Krejcikova.
Krejcikova continued her run and reeled off four straight points to move ahead, converting her first set point with another winner.
Gauff suddenly lost all momentum and Krejcikova quickly built a huge advantage, the teenager destroying her racket when she fell 4-0 down.
The American, to her credit, then showed some fight from 5-0 behind, winning three straight games and saving five match points in that sequence.
But Krejcikova kept a cool head and made no mistake with her sixth chance to seal the match, raising both arms after a famous victory that could launch her career.
Data Slam: Gauff falls apart
After having the better of much of the first set, Gauff struggled hugely in the middle of the match, losing seven straight games from 6-5 up in the first set to find herself 7-6 5-0 down in the second.
In the second set, Gauff only had five winners to 18 unforced errors and won only 10 of 21 first-serve points as frustration got the better of the youngster, meaning Krejcikova, who had fought so hard to claim the opener, did not have to produce any fireworks to get over the line.
Gauff – 25/41 Krejcikova – 27/28
Gauff – 4/7 Krejcikova – 5/8
BREAK POINTS WON
Gauff – 3/10 Krejcikova – 4/6
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